1. Field of the Invention
The present invention relates to an ElectroLuminescent (EL) device used as parts such as backlight of cellular phone, more particularly, to an EL device capable of reducing audio noise and electrical noise by alternating current power and a fabrication method of the EL device.
2. Description of Related Art
An inorganic EL (electroluminescent) device driven by alternating current power is possessed of electrical noise by characteristics of the alternating current power that is a driving power source. Particularly, a power source used in mobile phone is a direct current power, wherein transforming direct current power into a power source of sine wave similar to alternating current through an inverter and providing the transformed power source of sine wave to the EL device generally use the mobile phone. The transformed power source of sine wave used in the mobile phone generates electrical noise and audio noise as polarity of dielectric layer is being changed by alternating current power a phase of which is changed.
An EL device used as a backlight of a mobile phone, for example, comprises a transparent electrode layer that is formed of ITO and formed on a transparent insulation substrate such as PolyEthylene Terephthalate (PET) film as a first electrode, a luminescent layer and an insulation layer as a dielectric layer sequentially formed on the transparent electrode layer, a rear electrode layer as a second electrode formed on the insulation layer, and a protection layer formed to envelope the luminescent layer, the insulation layer and the rear electrode layer.
The EL device further comprises a ground electrode that is formed on the protection layer, and a dielectric rear tape that is formed on the ground electrode, wherein the ground electrode is formed of a copper plate, and the dielectric rear tape is adhered onto the ground electrode to insulate the ground electrode from the outside.
In such an EL device, the transparent electrode layer and rear electrode layer are used as two electrodes of front electrode and rear electrode respectively to be connected to an output terminal of an inverter, wherein AC power is supplied to the two electrodes. Furthermore, the ground electrode is grounded to a substrate. Therefore, the EL device has three terminals including two electrodes that are connected to the output terminal of the inverter and the ground electrode that is connected to a ground terminal.
The EL device transforms DC power of battery through the inverter and provides transformed sinusoidal AC power to the electrodes, since the DC power of battery is used as a power source of the EL device.
Therefore, light is emitted from the luminescent layer, if the sinusoidal AC power that is transformed through the inverter is supplied to the transparent electrode layer and the rear electrode layer that act as two electrodes in an EL device having the foregoing structure.
However, there have been problems in such an EL device in that electrical noise is generated by the AC power, and audio noise is generated from the dielectric layer as phase of an AC power is alternately being changed.
Furthermore, there have been problems in that although a copper plate used as the ground electrode is formed on the protection layer to reduce noise, the copper plate has to be adhered to the EL device through a separate process, and a ground electrode has to be formed additionally so that the additionally formed ground electrode is grounded to the substrate.
Furthermore, there have been problems in that since an insulation tape surely has to be adhered to the copper plate so that the insulation tape encircles the copper plate so as to insulate the copper plate from the outside, not only process is cumbersome and complex, but also it is difficult to apply the insulation tape to a device to which the insulation tape is not required to be adhered, or to which the insulation tape is partially adhered although it is possible to apply the insulation tape to a backlight of LCD (liquid crystal display) to all over the front of which the insulation tape is required to be adhered.